1. Field of the Invention
This invention relates to a computer, more particularly, to a compact computer such as a pocket computer, and a scientific calculator in which one or more expressions can be stored.
2. Description of the Prior Art
A conventional compact computer such as a pocket computer and a scientific electronic calculator has a memory for storing one or more algebraic expressions or formulae to be computed. In such a computer, an expression is previously reserved in the memory, a value of the variable(s) of the expression is input, and thereafter the computation of the expression is executed. More specifically, the processes are executed in such a computer as follows:
(a) The algebraic expression reserve (AER) mode is set, and a specific memory region is selected;
(b) An expression is input to be stored in the selected memory region;
(c) The mode is shifted from the AER mode to the computation mode;
(d) The expression to be computed is accessed from the memory region;
(e) A value of the variable in the expression is entered; and
(f) Computation of the designated formula is started by depressing the designated key.
When an expression to be computed has been already stored and the operation mode has been set to the computation mode, the computation of the expression is conducted following the above-mentioned processes (d) to (f), and thus, no problem is present in this case. Nevertheless, if the computation of a newly-stored expression is to be executed just after the expression to be computed has been stored (i.e., while the AER mode remains set), or if the computation of another previously-stored expression is to be executed while the AER mode still remains set, such a conventional computer has a problem as described below.
FIG. 5 illustrates a typical example of the key operation of a conventional scientific electronic calculator, for executing the computation of the expression sin A in which the numerical value (degree) stored in the A-memory is used as the variable of the expression. The way of the computation will be described by way of showing the process of the key operation.
(1) When a user depresses a second function [2ndF] key, and the algebraic expression reserve mode [AER]key, the mode of the calculator is shifted to the AER mode. An indication "AER" appears in a display the contents of which are shown in the right column of FIG. 5. The first expression memory region is automatically selected, and "1:" is shown in the display.
(2) An expression [f()=] key, an alphabet [ALPHA] key, an [A] key, and the expression [f()=] key are operated to designate the A-memory as the variable.
(3) A [SIN] key, the [ALPHA] key, the [A] key, and an expression input [ENT] key are operated to store the expression sin A in the first expression memory region.
(4) The [2ndF] key and the [AER] key are operated. The mode of the calculator is shifted from the AER mode to the computation mode.
(5) The [2ndF] key and a [1:] key are operated to select the computation of the expression stored in the first expression memory region. A prompt informing that a number is to be input in the A-memory which is the variable of the expression is indicated in the display.
(6) Numeral keys [3] and [0] and a computation [COMP] key are operated to enter the numerical value "30" into the A-memory. Thereafter, the computation of sin 30.degree. is conducted.
In such a conventional computer, the computation of a newly-stored expression just after the expression to be computed has been stored (i.e., while the AER mode remains set), or the computation of another previously-stored expression while the AER mode still remains set cannot be executed, until the mode is transferred from the AER mode to the computation mode and the expression to be computed is selected. As a result, a variety of keys should be operated before entering into the computation of an expression, thus causing much inconvenience to the user.